Various techniques are used for identifying users of data communication networks, for various purposes such as user authentication and characterization of surfing habits of web users. Web applications usually recognize a user by user-name and password. However, a user can be identified in some web applications by other identifiers such as a nickname or an e-mail address.
U.S. Patent Application Publication 2008/0285464, whose disclosure is incorporated herein by reference, describes a method for communication analysis that includes monitoring communication sessions conducted by entities in a communication network. Identifiers that identify the entities are extracted from the monitored sessions. The identifiers extracted from the sessions are grouped in respective identity clusters, each identity cluster identifying a respective entity. A subset of the identity clusters, which includes identifiers that identify a target entity, is merged to form a merged identity cluster that identifies the target entity. An activity of the target entity in the communication network is tracked using the merged identity cluster.